Buggy code:
public class AbstractDOMParser extends AbstractXMLDocumentParser { protected static final String NAMESPACES = ( Constants . SAX_FEATURE_PREFIX ) + ( Constants . NAMESPACES_FEATURE ) ; protected static final String CREATE_ENTITY_REF_NODES = ( Constants . XERCES_FEATURE_PREFIX ) + ( Constants . CREATE_ENTITY_REF_NODES_FEATURE ) ; protected static final String INCLUDE_COMMENTS_FEATURE = ( Constants . XERCES_FEATURE_PREFIX ) + ( Constants . INCLUDE_COMMENTS_FEATURE ) ; protected static final String CREATE_CDATA_NODES_FEATURE = ( Constants . XERCES_FEATURE_PREFIX ) + ( Constants . CREATE_CDATA_NODES_FEATURE ) ; protected static final String INCLUDE_IGNORABLE_WHITESPACE = ( Constants . XERCES_FEATURE_PREFIX ) + ( Constants . INCLUDE_IGNORABLE_WHITESPACE ) ; protected static final String DEFER_NODE_EXPANSION = ( Constants . XERCES_FEATURE_PREFIX ) + ( Constants . DEFER_NODE_EXPANSION_FEATURE ) ; private static final String [ ] RECOGNIZED_FEATURES = new String [ ] { AbstractDOMParser . NAMESPACES , AbstractDOMParser . CREATE_ENTITY_REF_NODES , AbstractDOMParser . INCLUDE_COMMENTS_FEATURE , AbstractDOMParser . CREATE_CDATA_NODES_FEATURE , AbstractDOMParser . INCLUDE_IGNORABLE_WHITESPACE , AbstractDOMParser . DEFER_NODE_EXPANSION } ; protected static final String DOCUMENT_CLASS_NAME = ( Constants . XERCES_PROPERTY_PREFIX ) + ( Constants . DOCUMENT_CLASS_NAME_PROPERTY ) ; protected static final String CURRENT_ELEMENT_NODE = ( Constants . XERCES_PROPERTY_PREFIX ) + ( Constants . CURRENT_ELEMENT_NODE_PROPERTY ) ; private static final String [ ] RECOGNIZED_PROPERTIES = new String [ ] { AbstractDOMParser . DOCUMENT_CLASS_NAME , AbstractDOMParser . CURRENT_ELEMENT_NODE } ; protected static final String DEFAULT_DOCUMENT_CLASS_NAME = "org.apache.xerces.dom.DocumentImpl" ; protected static final String CORE_DOCUMENT_CLASS_NAME = "org.apache.xerces.dom.CoreDocumentImpl" ; protected static final String PSVI_DOCUMENT_CLASS_NAME = "org.apache.xerces.dom.PSVIDocumentImpl" ; public static final RuntimeException abort = new RuntimeException ( ) ; private static final boolean DEBUG_EVENTS = false ; private static final boolean DEBUG_BASEURI = false ; protected DOMErrorHandlerWrapper fErrorHandler = null ; protected boolean fInDTD ; protected boolean fCreateEntityRefNodes ; protected boolean fIncludeIgnorableWhitespace ; protected boolean fIncludeComments ; protected boolean fCreateCDATANodes ; protected Document fDocument ; protected CoreDocumentImpl fDocumentImpl ; protected boolean fStorePSVI ; protected String fDocumentClassName ; protected DocumentType fDocumentType ; protected Node fCurrentNode ; protected CDATASection fCurrentCDATASection ; protected EntityImpl fCurrentEntityDecl ; protected int fDeferredEntityDecl ; protected final StringBuffer fStringBuffer = new StringBuffer ( 50 ) ; protected StringBuffer fInternalSubset ; protected boolean fDeferNodeExpansion ; protected boolean fNamespaceAware ; protected DeferredDocumentImpl fDeferredDocumentImpl ; protected int fDocumentIndex ; protected int fDocumentTypeIndex ; protected int fCurrentNodeIndex ; protected int fCurrentCDATASectionIndex ; protected boolean fInDTDExternalSubset ; protected QName fRoot = new QName ( ) ; protected boolean fInCDATASection ; protected boolean fFirstChunk = false ; protected boolean fFilterReject = false ; protected Stack fBaseURIStack = new Stack ( ) ; protected final QName fRejectedElement = new QName ( ) ; protected Stack fSkippedElemStack = null ; protected boolean fInEntityRef = false ; private QName fAttrQName = new QName ( ) ; protected LSParserFilter fDOMFilter = null ; protected AbstractDOMParser ( XMLParserConfiguration config ) { } protected String getDocumentClassName ( ) { } protected void setDocumentClassName ( String documentClassName ) { } public Document getDocument ( ) { } public void reset ( ) throws XNIException { } public void setLocale ( Locale locale ) { } public void startGeneralEntity ( String name , XMLResourceIdentifier identifier , String encoding , Augmentations augs ) throws XNIException { } public void textDecl ( String version , String encoding , Augmentations augs ) throws XNIException { } public void comment ( XMLString text , Augmentations augs ) throws XNIException { } public void processingInstruction ( String target , XMLString data , Augmentations augs ) throws XNIException { if ( fInDTD ) { if ( ( ( fInternalSubset ) != null ) && ( ! ( fInDTDExternalSubset ) ) ) { fInternalSubset . append ( "<?" ) ; <START_BUG> fInternalSubset . append ( target . toString ( ) ) ; <END_BUG> fInternalSubset . append ( '<seq2seq4repair_space>' ) ; fInternalSubset . append ( data . toString ( ) ) ; fInternalSubset . append ( "?>" ) ; } return ; } if ( AbstractDOMParser . DEBUG_EVENTS ) { System . out . println ( ( ( "==>processingInstruction<seq2seq4repair_space>(" + target ) + ")" ) ) ; } if ( ! ( fDeferNodeExpansion ) ) { if ( fFilterReject ) { return ; } ProcessingInstruction pi = fDocument . createProcessingInstruction ( target , data . toString ( ) ) ; setCharacterData ( false ) ; fCurrentNode . appendChild ( pi ) ; if ( ( ( ( fDOMFilter ) != null ) && ( ! ( fInEntityRef ) ) ) && ( ( ( fDOMFilter . getWhatToShow ( ) ) & ( NodeFilter . SHOW_PROCESSING_INSTRUCTION ) ) != 0 ) ) { short code = fDOMFilter . acceptNode ( pi ) ; switch ( code ) { case LSParserFilter . FILTER_INTERRUPT : { throw AbstractDOMParser . abort ; } case LSParserFilter . FILTER_REJECT : { } case LSParserFilter . FILTER_SKIP : { fCurrentNode . removeChild ( pi ) ; fFirstChunk = true ; return ; } default : { } } } } else { int pi = fDeferredDocumentImpl . createDeferredProcessingInstruction ( target , data . toString ( ) ) ; fDeferredDocumentImpl . appendChild ( fCurrentNodeIndex , pi ) ; } } public void startDocument ( XMLLocator locator , String encoding , NamespaceContext namespaceContext , Augmentations augs ) throws XNIException { } public void xmlDecl ( String version , String encoding , String standalone , Augmentations augs ) throws XNIException { } public void doctypeDecl ( String rootElement , String publicId , String systemId , Augmentations augs ) throws XNIException { } public void startElement ( QName element , XMLAttributes attributes , Augmentations augs ) throws XNIException { } public void emptyElement ( QName element , XMLAttributes attributes , Augmentations augs ) throws XNIException { } public void characters ( XMLString text , Augmentations augs ) throws XNIException { } public void ignorableWhitespace ( XMLString text , Augmentations augs ) throws XNIException { } public void endElement ( QName element , Augmentations augs ) throws XNIException { } public void startCDATA ( Augmentations augs ) throws XNIException { } public void endCDATA ( Augmentations augs ) throws XNIException { } public void endDocument ( Augmentations augs ) throws XNIException { }

Fix:
fInternalSubset . append ( target ) ;